Backend powering ContentModel.io

Check https://github.com/OriginalEXE/ContentModel.io-web for the roadmap, discussion etc.

List of required environment variables:

AUTH0_DOMAIN
AUTH0_CLIENT_ID
AUTH0_CLIENT_SECRET
AUTH0_AUDIENCE
PORT
DATABASE_URL
HOST
FRONTEND_URL
LOCAL_SSL_KEY_PATH
LOCAL_SSL_CERT_PATH
CLOUDINARY_URL
NODE_ENV
REMOTE_PUPPETEER
PRIVATE_CONTENT_MODEL_SCREENSHOT_SECRET